In recent years, as image-recording materials, materials for forming color images have been predominant and, specifically, recording materials for an ink jet system, recording materials for a thermal transfer system, recording materials for an electro-photographic system, transfer type silver halide light-sensitive materials, printing inks, and recording pens have found widespread use. Also, in photographing devices such as CCDs for photographing equipment, and in LCDs and PDPs for display, color filters are used for recording or reproducing a color image. In these color image recording materials and color filters, colorants (dyes or pigments) of three primary colors of a so-called additive color mixing process or subtractive color mixing process have been used in order to display or record full-color images. In actuality, however, there is no fast colorant having the absorption characteristics capable of realizing a preferred color reproduction region and resisting various use conditions and environmental conditions. Thus, the improvement thereof has strongly been desired.
Dyes or pigments to be used for the above-mentioned uses are required to have in common the following properties. That is, they are required to have absorption characteristics favorable in view of color reproduction and have good fastness under the conditions of the environment wherein they are used, for example, fastness against light, heat, and an oxidative gas such as ozone. In addition, in the case where the colorant is a pigment, the pigment is further required to be substantially insoluble in water or in an organic solvent, to have a good fastness to chemicals, and not to lose the preferred absorption characteristics it shows in a molecularly dispersed state even when used as particles. Although the required properties described above can be controlled by adjusting the intensity of intermolecular interaction, both of them are in a trade-off relation with each other, thus being difficult to allow them to be compatible with each other. Besides, in the case of using a pigment as the colorant, the pigment is additionally required to have a particle size and a particle shape necessary for realizing desired transparency, to have good fastness under the conditions of the environment wherein they are used, for example, fastness against light, heat, and an oxidative gas such as ozone, to have good fastness to an organic solvent and chemicals such as a sulfurous acid gas, and to be capable of being dispersed in a used medium to a level of fine particles, with the dispersed state being stable. In particular, there is a strong demand for a pigment which has a good yellow hue and is fast to light, moist heat, and active gases in the environment, particularly for a pigment having high tinctorial strength and is fast against light.
That is, in comparison with a dye which is required to have properties as colorant molecules, the pigment is required to have more properties, i.e., it is required to satisfy all of the above-mentioned requirements as a solid of an aggregate of a colorant (dispersion of fine particles) as well as the properties as molecules of a colorant molecule. As a result, a group of compounds which can be used as pigments are extremely limited in comparison with dyes. Even when high-performance dyes are converted to pigments, few of them can satisfy requirement for the properties as a dispersion of fine particles. Thus, such pigments are difficult to develop. This can be confirmed from the fact that the number of pigments registered in Color Index is no more than 1/10 of the number of dyes.
Azo pigments are excellent in hue and tinctorial strength which are characteristics of coloring, and hence they have widely been used in printing inks, ink for an inkjet system, and electro-photographic materials. Of the pigments, the most typically used pigments are yellow diarylide pigments and red naphthol azo pigments. Examples of such diarylide pigments include C.I. pigment yellow 12, C.I. pigment yellow 13, and C.I. pigment yellow 17. Examples of such red naphthol azo pigments include C.I. pigment red 208, and C.I. pigment red 242. However, these pigments are inferior in fastness, particularly light fastness, and hence they are decomposed when prints printed by them are exposed to light, thus being inappropriate for prints which are to be stored for a long lime.
In order to remove such defects, there have been disclosed azo pigments having a fastness improved by increasing molecular weight or by introducing a group having a strong intermolecular interaction (see, for example, patent documents 1 to 3). However, even the improved pigments, for example, the pigments described in patent document 1 have the defect that they have still insufficient light fastness though improved to some extent, and pigments described in, for example, patent documents 2 and 3 have a greenish hue and a low tinctorial strength, thus being inferior in coloring characteristics.
Also, patent documents 4 to 7 disclose colorants which have absorption characteristics of excellent color reproducibility and have a sufficient fastness. However, some of the specific compounds described in the patent documents show poor fastness though showing good hue, and some of them show poor hue though showing good fastness. Also, some dissolve in water or in an organic solvent, thus being insufficient in fastness against chemicals.
In the case of expressing a full-color image based on the primary color mixing process using three colors of yellow, magenta, and cyan or using four colors further including black, use of a pigment for only one color, the pigment having an inferior fastness would change gray balance of the prints with the lapse of time, and use of a pigment having inferior coloring characteristics would reduce color reproducibility upon printing. Thus, in order to obtain prints which can maintain high color reproducibility for a long time, there have been desired a yellow pigment and a pigment dispersion which have both good coloring characteristics and good fastness.
Azo colorants have conventionally been utilized in various fields since they absorb various visible lights. For example, they have come into use in such various fields as coloring of synthetic resins, printing inks, colorants for sublimation type thermal transfer materials, inks for inkjet recording, and colorants for color filters. Important performance required for azo colorants as colorants includes absorption spectrum. Hue of a colorant exerts a great influence on color tone and feeling of a body colored with the colorant, giving a large effect on visual sensation. Therefore, there have long been made studies on absorption spectrum of a colorant.
Conventionally known azo dyes containing a nitrogen-containing, 5-membered ring as an azo component are also disclosed in patent documents 8 and 9. Also, patent document 10 discloses naphthol series azo pigments wherein a benzene ring and a naphthalene ring are connected to each other through an azo group.    Patent document 1: JP-A-56-38354    Patent document 2: U.S. Pat. No. 2,936,306    Patent document 3: JP-A-11-100519    Patent document 4: WO05/52074    Patent document 5: WO00/023525    Patent document 6: JP-A-2008-13472    Patent document 7: JP-T-9-511278 (the term “JP-T” as used herein means a published Japanese translation of a PCT application)    Patent document 8: JP-A-55-161856    Patent document 9: JP-A-2008-7732    Patent document 10: JP-A-2004-123866